A certain number of pressure sensors, for measuring the pressure of a gas that is below atmospheric pressure, are known.
U.S. Pat. No. 5,633,465 describes a Pirani-type pressure sensor based on an electric conductor or semiconductor. The electric conductor is immersed in the gas the pressure of which is measured. The electric conductor is heated to a temperature above the temperature of the gas in which it is immersed. The electric conductor loses heat by conduction to the molecules of gas in which it is immersed. The heat flux exchanged between the electric conductor and the gas is higher or lower according to the pressure of this gas, the thermal conductivity of which varies with pressure. As a result, the temperature of the electric conductor varies as a function of the gas pressure. The electrical resistance of the conductor is modified by this variation in temperature. A circuit measures this electrical resistance. This circuit therefore determines the pressure of the gas as a function of the electrical resistance measured.
Such a sensor relies on the temperature coefficient of resistance of materials of which the electric conductor is made. As this coefficient is usually below 1%, the sensor has low sensitivity. Furthermore, the measurement range of this sensor is limited. This is because since the electric resistance varies weakly with pressure, the noise on the measurement of the resistance has an order of magnitude close to the variation in resistance induced by the variation in pressure when the pressures to be measured are below 10−2 Pa or above 104 Pa.
Document US20110107838 describes a pressure sensor of the MEMS type with mechanical resonance. This sensor comprises a vibrating beam suspended in the gas the pressure of which is measured. The beam is actuated by electrodes. A variation in gas pressure modifies the mechanical quality factor of the beam. The frequency of mechanical resonance of the excited beam and the amplitude of oscillation thereof are therefore modified. By analysing the movement of the beam, the document deduces its mechanical resonant frequency thereof and from this extrapolates the gas pressure.
Such a sensor has the disadvantage of operating over only a fairly narrow operating range and is not suited to measure high levels of vacuum (pressures of below 10−1 Pa for example).
Document EP0144630 describes, amongst other things, a pressure measurement device. In one example, a liquid-crystal cell is excited by a light source. Liquid crystal reflection spikes are measured in order to deduce a temperature of a surrounding fluid, the reflected wavelength varying with this temperature. The liquid crystal cell forms a Bragg reflector and not an electromagnetic resonator.
Document EP1944595 describes a gas pressure measurement device based on an acoustic resonator. Such a device has a limited accuracy and a limited measurement range.
Document WO2012/103942 describes a gas pressure measurement device, likewise based on an acoustic resonator. Such a device therefore also has a limited accuracy and a limited measurement range.
Thus, no satisfactory solution for offering high sensitivity, with a broad pressure measurement range and a relatively simple and easy-to-produce structure has been identified.